Patent GB-1181424-A (GB)
Title: Improvements in or relating to Automatic Telephone Exchanges
Inventor: ATTWELL BRIAN ERNEST
IPC: H04Q3/00
Filed: 1967-10-12
Abstract: 1,181,424. Automatic exchange systems. GENERAL ELECTRIC & ENGLISH ELECTRIC CO'S. Ltd. 11 Oct., 1968 [12 Oct., 1967], No. 46592/67. Heading H4K. In an exchange utilizing a reed relay switching network having both local lines and trunks connected to its inlets and having its outlets interconnected by link circuits, each of the latter is equipped to supervise both local and trunk calls and can thus remain in use irrespective of the type of call that a local subscriber may require. The exchange may be a local exchange, a PBX having direct outward dialling facilities or a discriminating selector repeater to a parent exchange. Particular description. Originating calls, Fig. 1.-Initiation of a call by a local subscriber causes his line circuit 1 to be connected via the A, B and C stages of switching network 5 to a free link circuit 4 under the control of identifier 2 and control circuit 3. The latter also sets up a connection between the link circuit 4 and a free register 6 via a two-stage, reed relay register connector 7. The register reverts dial tone and then accepts dialled digits from the caller. If the digits indicate a local subscriber, a path thereto from link 4 is set-up via the D, C, B and A stages of network 5 and a long burst of ringing current and tone are transmitted in the appropriate directions from a source common to the registers. (Each link has two appearances at the registers so that line splitting can be effected.) At the termination of this ringing burst, further ringing is effected from generators in the link circuit and the register is dismissed. If the wanted party is busy, busy tone is reverted from the register. If the dialled digits indicate an outgoing call, a path via the D, C, B and A stages is set up to a free junction in the required direction and further digits are repeated thereto either directly or after storage in the register. The latter releases immediately in the former case. For the local call the link provides the usual answer and clearing detection facilities in the form of reed relay sets, a transformer transmission bridge and time-metering facilities and, in addition, for outgoing calls it provides facilities for reception of metering pulses over the junction, digit repetition (e.g. a D.C. by-pass round the transformer) and operator "manual hold". Incoming calls.-Seizure of an incoming supervisory unit 10 causes identifier 2 and control 3 to set up a priority connection from the unit to a register via register connector 7. The register recognizes the received digits as being in respect of a terminating call or a transit call and thereby instructs the control circuit to set up a path via the D, C, B, and A stages to a local line 1 or to an outgoing junction 8 or 9 as appropriate. Discriminator selector working.-In this case all originating calls are initially connected via the A, B, C stages, a link circuit 4 and the D, C, B, A stages to a free junction 8 to the parent exchange as well as via the same link to a register. The latter discriminates the dialled digits, repeating them to the parent if appropriate or causing the initial connection to junction 8 to be released in favour of a new D. C. B. A connection to another junction 9 or to a local line if this is warranted. The subsequent actions are as described in the preceding paragraphs. Prior art.-In one known system, Fig. 2, a calling line is initially connected to a register via an outgoing junctor 13, this connection being possibly dropped in its entirety and another connection to an alternative outgoing junctor 14 or to a local junctor 15 being set up in accordance with the digits dialled. Tandem calls in such an exchange involve an incoming supervisory unit 16, the switching network 12 and an appropriate junctor 13, 14, the transmission bridge in the incoming unit being switched out of circuit for the duration of the call. In another known system, Fig. 3, a calling line is connected via a register access unit 16 to a register and then to an appropriate junctor via the switching network 17. As with the other known exchange, terminating calls utilize the transmission bridge and ringing facilities of an incoming supervisory unit 21 whereas tandem calls dispense with these facilities. The outgoing and local junctors 18, 19, 20 are provided only with the facilities required for the type of call that they handle. They are allotted on the basis of the expected number of calls in any particular direction whereas the supervisory units of the present invention are provided on the basis of the expected number of originating calls whereby changes in the calling habits of the local subscribers are accommodated without any wiring changes in the exchange.